Multi GNSS PPP analysis on SWEPOS reference stations
Examensarbete för masterexamen
The Swedish mapping, cadastral and land registration authority, Lantmäteriet, has a permanent network of GNSS stations, SWEPOS, which can be used as reference stations in differencing and RTK. A limiting factor in the RTK service is, or soon will be, related to local, station dependent effects. This study has utilized the carrier phase residuals for GPS and Galileo from the multi-GNSS PPP software GipsyX to analyze the surrounding environment and local effects around 42 SWEPOS stations. 21 of the stations are concrete pillars and 21 are steel grid masts and there exists one of each at each of the locations, which ranges from the southern part of Sweden to the north. The carrier phase residuals were successfully utilized to describe local phenomena such as wooden fences, adjacent houses and multipath from solid bedrock. There was however an effect that was only present for one station, VIS6, that could not be explained. Its residuals at high elevation, 45° - 90°, followed those of the elevation angle circles instead of the satellites’ orbits. It was illustrated and shown with examples that it is useful to analyze stations in pairs. It helps to discredit certain error sources and phenomena that should be affecting both of the stations. It was furthermore illustrated that it is useful to study the monthly mean residuals as a function of elevation angle in parallel with the skyplots. The steel grid mast stations were furthermore analyzed with respect to coordinate repeatability and it was found that the highest performance were achieved with the combination of GPS+GLONASS+Galileo. The achieved repeatabilities (standard deviation) for the latitudinal, longitudinal and vertical components were 1.20mm, 3.56mm and 4.00mm, respectively. The coordinate accuracies for GPS, GPS+Galileo and GPS+GLONASS were within the GPS+GLONASS+Galileo repeatability. Their respective repeatabilities differs to that of GPS+GLONASS+Galileo by sub-millimeter levels, which means that any of the combinations yields comparable results.
GNSS, PPP, GipsyX, repeatability, solution offsets, carrier phase residuals, multipath.